An ion exchange membrane method using an electrolysis tank equipped with an ion exchange membrane is mainly used in the electrolytic decomposition (hereinafter, referred to as the “electrolysis”) of an aqueous solution of alkali metal chloride such as brine. This electrolysis tank is equipped with a large number of electrolysis cells connected in series therein. Electrolysis is performed by interposing an ion exchange membrane between the respective electrolysis cells. A cathode chamber having a cathode and an anode chamber having an anode are disposed back to back via a partition wall (rear plate) in the electrolysis cell. As an electrolysis tank, an electrolysis tank described in Patent Literature 1 or the like is known.
In recent years, the facility of an electrolysis tank has been increased in size, and the number of electrolysis cells arranged in series has increased to from about 100 to 200 pairs. Along with it, the reverse current (current flowing in the direction opposite to the electrolytic current) generated at the time of stopping has increased, and thus the degradation due to the oxidation of the cathode easily occurs.
In order to prevent the degradation of the cathode, a measure in which a weak protection current is applied before stopping the electrolysis tank has been adopted. However, there is a problem that the cost of electrolysis increases since the operation is complicated and incidental facilities are required in this electrolysis stopping method of applying the protection current. These are points to be desirably improved from an economic point of view. For this reason, a method to prevent the degradation of the cathode without applying the protection current at the time of stopping the electrolysis tank is desirable.
As a technique to prevent the degradation of the cathode by the reverse current, it is disclosed in Patent Literature 2 a cathode structure for electrolysis in which Raney nickel is formed on the surface of a current collector by dispersion plating.